The invention relates to a display panel with light emitting diode array forming typically an electroluminescent display and it relates more particularly to such a panel both more economic and more luminous than similar systems, while allowing faster display.
A conventional electroluminescent display is formed of an array of light emitting diodes, a corresponding number of members (typically bistable flip flops) inserted between said diodes and a shift register in which flows the information representative of an image to be displayed. This information is delivered at the timing of a clock by a control unit associated with a programme memory. The control unit and the programme memory are generally situated in a case separate from the panel and connected to this latter by a strand of conducting wires. This arrangement is advantageous when the diode panel is intended to be placed outside and subjected to bad weather. In this case, the most fragile components contained in the control unit may be placed in a sheltered position and more readily accessible for modification or updating the messages to be reproduced. Up to now, it has been fairly difficult to adapt the characteristics of the memories to those of the light emitting diodes. Thus attempts have been made to supply the diodes through load resistors, but this type of circuit has the drawback of power consumption in the resistors which is not directly useful for the display. The cost price is moreover high, not only because of the number of resistors required but also because of the labour cost for wiring them. Attempts have been made to supply the light emitting diodes directly by the current delivered by the memories, But that generally results in causing said memories to work outside the characteristics provided by the constructor of these integrated circuits. Such a method of construction is, at the limit, conceivable for displaying moving messages, for the diodes are used only for a small part of the time. This becomes more difficult to contemplate for displaying fixed messages, particularly graphic images, where some diodes may be permanently lit for relatively long periods of time, whence much more unfavourable operating conditions for the memories which supply them.